The partitioning (or sorption) of trace elements from aqueous solutions onto mineral surfaces and natural organic matter (NOM) has played a major role in determining the trace element content of natural waters. This review examines sorption processes on mineral surfaces for nine trace elements (Cr, Co, Ni, Cu, Zn, Sr, Cd, Hg, Pb), focusing on the results of modern x-ray spectroscopic studies. Such studies provide unique information on the structure and composition of sorption products, including their mode of attachment to mineral surfaces or functional groups in NOM under in situ conditions (i.e., with aqueous solution present at 25°C). The types of chemical reactions (acid-base, ligand exchange, redox, dissolution/reprecipitation) that can occur at mineral-aqueous solution interfaces are also reviewed, and some of the factors that affect the reactivity of mineral surfaces are discussed, including changes in the geometric and electronic structures of mineral surfaces when they first react with aqueous so...

Sorption of Trace Elements on Mineral Surfaces: Modern Perspectives from Spectroscopic Studies, and Comments on Sorption in the Marine Environment

Recent studies on the speciation of Zn in contaminated soils confirmed the formation of Zn-layered double hydroxide (LDH) and Zn−phyllosilicate phases. However, no information on the kinetics of th...

Changes in Zinc Speciation in Field Soil after Contamination with Zinc Oxide

Oxide surfaces as environmental interfaces

http://xraysweb.lbl.gov/uxas/Publicatons/Papers/pdfs/Toner_biogenic_Mn.pdf

Zinc sorption to biogenic hexagonal-birnessite particles within a hydrated bacterial biofilm

Surface complexation and precipitate geometry for aqueous Zn(II) sorption on ferrihydrite I: X-ray absorption extended fine structure spectroscopy analysis

The local structure of Cd(II) surface complexes adsorbed onto manganite (γ-MnOOH) has been investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy. Adsorption experiments were carried out within the pH range 7.4–9.8 and with surface coverage from 2.2 to 8.9 μmol/m2. Quantitative analysis of the EXAFS spectra shows little difference in the local coordination environment of Cd regardless of the coverage. Analysis of the first shell required a third cumulant in an asymmetric distribution model (i.e., non-Gaussian distribution), indicating distorted CdO6 octahedra with an average Cd–O distance of 2.31 A. A single second shell of Mn neighbors at a constant distance of 3.33 A was detected. This comparatively short distance shows that inner-sphere complexes are formed. No Cd neighbor was found which means that cadmium hydroxide precipitation or cluster formation does not occur at the surface at the experimental conditions probed in this study. We assign the Cd–Mn distance to edge sharing between CdO6 and MnO6 octahedra, with a geometry similar to that in the mixed solid Cd2Mn3O8. This adsorption mode is possible on the {110} and {010} cleavage planes of manganite.

Laurence Bochatay

Papers

Metal Ion Coordination at the Water–Manganite (γ-MnOOH) Interface: II. An EXAFS Study of Zinc(II)